Vanadium Alloys with Improved Resistance to Helium Embrittlement

A series of experimental vanadium alloys have been designed with small MC-type carbides in their microstructures to trap helium produced during neutron irradiation, thereby reducing helium embrittlement. The tensile properties and fabricability of the alloys were strongly influenced by the amounts of metal carbide (MC)-forming elements, especially carbon. Alloys with 0.05 and 0.10 wt% carbon exhibited slightly lower yield strengths at 420 to 600°C than vanadium alloys such as V-5Cr-5Ti, Vanstar-7, V-3Ti-lSi, and V-15Cr-5Ti. However, this characteristic may actually be an asset from the standpoint of resistance to irradiation hardening. After implantation with 300 atomic parts per million (appm) 3He, both the V-Ti-C and V-Ti-Zr-C alloys exhibited less ductility losses at 600°C than the other vanadium alloys tested under comparable conditions. Examination of the experimental alloy microstructures by analytical electron microscopy (AEM) showed that the small MC-type carbides did, in fact, trap helium and that they were responsible for the increased resistance to helium embrittlement of these alloys.